The present invention relates to a method for operating a furnace with a multi-burner system for generating hot gas, particularly a gas turbine, preferably of a power plant.
A furnace, for example, a gas turbine, normally has a combustion chamber with multiple burners. Moreover, it is often the case that a fuel supply system is provided by means of which fuel is fed to the burners.
With an eye towards the ever more stringent regulations pertaining to the mandatory limit values for the emission of pollutants, efforts are made to operate the burners under the leanest conditions possible, that is to say, with a marked excess of oxidant, usually air. Such lean operation is able to considerably reduce particularly the formation of especially toxic NOx emissions. The lean combustion concurrently causes the combustion reaction to approach its lean extinguishing limit. Therefore, in order to keep pollutant emissions to a minimum, efforts are geared towards operating the gas turbine or its combustion chamber as close to the lean extinguishing limit as possible. For this purpose, with a conventional operating method, the fuel feed has to be adjusted as a function of various boundary conditions. The boundary conditions normally observed are, for instance, the ambient temperature, the relative humidity, the momentary air mass flow rate, which is particularly dependent on the degree of contamination of a compressor located upstream from the combustion chamber, the switching position (“ON” or “OFF”) of a fuel or air preheater, the composition of the fuel currently being used and so forth. The control of the fuel supply system is particularly complex when the boundary conditions taken into account vary. For example, as a rule, the ambient temperature and/or the fuel composition tend to vary over the course of the day during operation of the gas turbine. Since the individual boundary conditions affect the stability of the combustion procedure in different ways, it is not always possible to find a setting for the fuel feed that allows a stable operation of the individual burners close to the lean extinguishing limit. In order to nevertheless ensure proper operation of the gas turbine, which is of the utmost priority in power plants used to generate electricity, it is regularly accepted that the combustion chamber is operated at a certain safety margin from the lean extinguishing limit, and consequently, the higher pollutant emissions that inevitably result from this also have to be accepted.